In a small pot, bring the coconut milk and lemongrass to a simmer; cook for a few minutes, then remove from the heat and let steep for 1 or 2 hours. Strain and keep warm.

In a medium pot, heat the oil and butter over medium heat. When the foam subsides, add the rice and cook for a minute, stirring to coat well. Add about half the coconut milk and cook, stirring often, until it is absorbed. Add remaining coconut milk and then the regular milk about ½ cup at a time, cooking and stirring the rice after each addition until it is absorbed. Add the sugar with the last addition and cook until it dissolves and the milk is absorbed by the rice. If the rice is still too firm at the core, continue adding milk and cook until it has the texture you want. It should be a bit creamy, like a stovetop rice pudding. Stir in raisins if you’re using them, and serve warm. Serves 6.